Perennial Forages for Saline Seeps

Planting perennial forages into saline seep areas is one of several recommended practices for salinity control (see the factsheet Dryland Saline Seeps: Types and Causes, Agdex 518-12, published by Alberta Agriculture and Food).

Saline seeps result when salt-laden groundwater rises to within a few metres of the soil surface. Once the water is in the soil’s capillary zone, evaporation as well as cohesive and adhesive forces act like the wick in a kerosene lamp to draw saline water into the root zone or topsoil. Water then evaporates and the salts remain, gradually accumulating over time.

Forage establishment is especially tough in saline environments because of the harsh soil conditions for germination and emergence, along with heavy competition from salt-tolerant species like kochia or foxtail barley. Forages differ in their salinity and flood tolerance, with several appropriate species available depending on the specific farm situation.

How These Controls Work

Perennial forages help control salinity by lowering the existing groundwater, which allows salts to flush downward in the soil profile, depending on the dynamics associated with groundwater recharge (see Dryland Saline Seeps: Types and Causes, Agdex 518-12).

The forages also provide soil cover and shading to help reduce evaporation, thereby reducing the capillary rise of salty water compared with bare soil areas. These controls are only possible when the salt concentration in the seep is not so high as to completely prevent all plant growth.

Perennial forages are an effective way to help control seep expansion, but they cannot reclaim the area for annual crop production unless the groundwater source is controlled first.

Plant Species

The choice of which salt tolerant forage or forage mixes to grow will depend on the desired land use for the affected area. For example, species like tall wheatgrass or Nuttall’s salt grass may be suitable for reclamation or wildlife habitat, but if livestock production is the goal, then forage mixes should include productive, long lived and relatively palatable species more suitable for grazing or hay production.

Forage mixes are often recommended because of the extreme variability and dynamic nature encountered within typical saline seeps. Some forage species can establish in strongly saline zones while others are more suitable as livestock forage with moderate salinity tolerance. Soil testing will give a good indication of the range of salinity in terms of electrical conductivity (EC). Table 1 shows the relationship between the salinity rating and EC values.

* dS/m = deciSiemens per metre, a unit of measure for electrical conductivity within a saturated soil paste extract from the soil.

Table 2 lists the characteristics of various salt-tolerant grass species recommended for seeding into saline seeps. A degree of flood tolerance is usually a requirement because saline areas are often temporarily saturated in the spring.

Some of the sod-forming species like green wheatgrass and creeping foxtail, once established, have the ability to creep into adjacent areas and can also choke out salt tolerant weeds like kochia or foxtail barley. Note that creeping foxtail is only moderately salt-tolerant in the seedling stage and, thus, may be difficult to establish. It also has poor drought tolerance.

Slender wheatgrass is recommended only when mixed with another grass species. It is quick to establish, so it provides good cover while the main grass species becomes established. However, slender wheatgrass will die out within two or three years, once the main grass is established. If possible, plant slender wheatgrass and the main species in separate rows.

If the area is severely saline, very salt-tolerant forages like Nuttall’s alkali grass can be established for reclamation purposes. However, this species is not suitable for livestock forage production.

Note that alfalfa seedlings are only slightly to moderately salt-tolerant, even though mature alfalfa can be moderately to strongly salt-tolerant. Thus, alfalfa is not suitable for planting into saline seep areas. Many of the common seed industry mixes include some alfalfa, but it will usually only establish on the slightly saline seep edges.

Table 2. Grass species recommended for seeding into saline seeps

Species

Salinity tolerance*

Sod or bunch

Rate of establishment

Longevity

Winterhardiness

Flood tolerance

Drought tolerance

Livestock palatability

creeping foxtail

high

sod

average

long

good

high

poor

good

meadow foxtail

medium

sod

average

long

good

high

poor

fair

smooth bromegrass

medium

sod

slow

long

excellent

medium

good

good

meadow bromegrass

medium

sod

slow

long

excellent

medium

good

good

slender wheatgrass

high

bunch

very fast

short

good

medium

good

fair

intermediate wheatgrass

medium

sod

fast

short

excellent

medium

good

good

pubescent wheatgrass

medium

sod

fast

short

excellent

medium

good

good

tall wheatgrass

high

bunch

fast

long

excellent

high

poor

poor

western wheatgrass

high

sod

fast

long

excellent

high

good

good

NewHy wheatgrass

high

sod

average

long

excellent

medium

good

good

green wheatgrass

high

sod

average

long

excellent

medium

good

good

Russian wildrye

high

bunch

very slow

long

good

poor

good

good

altai wildrye

high

bunch

very slow

long

excellent

medium

good

fair

beardless wildrye

very high

sod

very slow

long

good

medium

good

fair

Nuttall’s alkali grass

very high

sod

average

long

good

medium

good

very poor

* Salinity tolerance: medium - tolerates up to 6 to 8 dS/m, high - tolerates up to 8 to 12 dS/m, very high - tolerates greater than 12dS/m.Source: Adapted from original by Henry Najda, Alberta Agriculture and Food.

Forage Nutritional Issues

Care should be taken when feeding crops grown in saline seeps to livestock. Research by Agriculture and Agri-Food Canada has shown that high levels of sulphate and trace metals are common in plants grown in saline seeps. If there is any concern about forage quality, the feed should be tested and reviewed by a livestock nutritional specialist.

Hay Mixes

When selecting a mix for hay production, choose grasses that can be harvested easily. Low growing or basal growth grasses are difficult to swath and bale.

Grazing Mixes

Select forage species that are suited to the conditions in the seep and to your grazing needs. Wheatgrasses are good choices for spring pasture due to their lush spring growth, but become coarse and rank in the late summer and fall. Wildrye grasses are good choices for fall pasture because they usually start slowly in the spring, but produce good forage and cure well on the stem.

Stand Establishment

Establishing vegetation on a saline seep can be very difficult. One option is to seed in the fall when the seeps are dry and accessible. Seeding rates for saline seeps should be double those for non-saline areas. Several salt-tolerant forage mixtures are available from different seed suppliers, each with suggested planting rates.

For all types of saline seeps, plant salt-tolerant grasses in an area larger than the visibly saline area to ensure good control. For saline sloughs and depression bottom seeps, plant salt-tolerant grasses in a band around the saline wetlands. This band should cover the visibly saline area and extend an additional 20 to 60 metres further. Perennial Forage Establishment in Alberta (Agdex 120/22-3) is a good information source related to forage stand establishment.